1. Field of the Invention
The present inventive subject matter relates to a system including a high pressure, high temperature apparatus. In particular, the present inventive subject matter relates to a system and a high pressure, high temperature apparatus suitable for producing synthetic diamonds.
2. Description of the Prior Art
Synthetic diamonds are manufactured by a process of applying extreme pressure (e.g., 65 kilobars) to a quantity of a carbon source disposed within a container, and heating the container under pressure to a sufficient temperature wherein the diamond is thermodynamically stable. A high pressure, high temperature apparatus is often used to apply the necessary pressure and heat to the carbon source to achieve conversion of the graphite to the more thermodynamically stable diamond.
The synthesis of diamond crystals by high pressure, high temperature processes has become well established commercially. Diamond growth in high pressure, high temperature processes occurs by the diffusion of carbon through a thin metallic film of any of a series of specific catalyst-solvent materials. Although such processes are very successfully employed for the commercial production of industrial diamond, the ultimate crystal size of such diamond growth is limited by the fact that the carbon flux across the catalyst film is established by the solubility difference between graphite and the diamond being formed. This solubility difference is generally susceptible to significant decrease over any extended period due to a decrease in pressure in the system and/or poisoning effects in the graphite being converted.
While most commercial processes for synthesizing diamonds produce small or relatively small particles, there are processes known for producing much larger diamonds. These processes generally involve producing the diamond in a reaction vessel in which a predetermined temperature gradient between the diamond seed material and the source of carbon is created. The diamond seed material is at a point at which the temperature of the reaction medium will be near the minimum value while the source of carbon is placed at a point where the temperature will be near its maximum. A layer of diamond nucleation suppressing material and/or an isolating material is interposed between the mass of metallic catalyst/solvent and the diamond seed material.
By very carefully adjusting pressure and temperature and utilizing relatively small temperature gradients with extended growth times, larger diamonds can be produced by using the high pressure, high temperature apparatus. Attempts to reliably produce very high quality diamond growth, however, have presented a number of mutually exclusive, yet simultaneously occurring problems. These problems include the strong tendency for spontaneous nucleation of diamond crystals near the diamond seed material (which occurs with an increase in the temperature gradient over the “safe” value). If the growth period is extended to produce diamond growth from the seed of greater than about 1/20 carat in size, the nucleated growth competes with the growth from the diamond seed with subsequently occurring collisions of multiple crystals that result in stress fractures within the grown crystals. Another problem is the partial or complete dissolution of the diamond seed material in the melted catalyst-solvent metal during that part of the process in which the catalyst-solvent medium becomes saturated with carbon from the nutrient source and then melts. Such dissolution produces uncoordinated diamond growth proceeding from spaced loci, which growths upon meeting, result in subsequent confused, flaw-filled growth of the diamond crystal.
In addition to overcoming the problems of spontaneous nucleation of diamond and diamond seed dissolution, it is highly desirable to be able to exercise reproducible control over the diamond growth process and, thereby, be able to produce novel diamond products, e.g. diamonds having unique color patterns and characteristics as well as affording the possibility of optimizing one or more physical properties in a given diamond.
Many apparatuses and systems have been developed for making synthetic diamonds with the aim of producing stones of unique color and characteristics. For example, Kendall, in U.S. Pat. No. 3,914,078, discloses generation of ultra-high pressures by a pair of opposed Bridgeman-type anvils. The generation of pressure is improved by surrounding the major portions of each anvil with a frustro-conical segmented jacket in position to transmit vertical forces thereon to the anvils in an axial direction and at the same time induce lateral compressive stresses therein for increasing the resistance thereof to brittle failure. Additional support is provided to the pressure-face ends of the anvils by a die ring laterally disposed therebetween in position to be circumferentially stressed by a segmented die ring which is, in turn, similarly compressed by a band of pressure-transmitting metal subjected to lateral extrusion by an annular piston enclosing the pressure system. The displacement of the piston is adjustably controlled in accordance with the size of the anvils and the axial forces thereon to provide optimum support to the die ring.
Strong, in U.S. Pat. No. 4,301,134, discloses diamond crystals of controlled impurity content and/or impurity distribution and reaction vessel configurations for the production thereof. Combinations of “dopant”, “getter” and “compensator” materials are employed to produce gem stones of unusual color patterns, or zoned coloration, using specific reaction vessel configurations. The reaction vessel configurations include a pair of punches and an intermediate belt or die member. The die member defines a centrally-located aperture and, together with the punches, defines two annular volumes to which pressure may be applied.
Ishizuka, in U.S. Pat. No. 4,518,334, discloses a high temperature high pressure apparatus which comprises: an annular die having a straight cylindrical bore and a substantially conical face in adjacency outwards with each end thereof, a pair of tapered punches which are in opposed and axial alignment with the die so that a conical face of each punch is substantially in parallel with that of the die, a pair of inner gaskets, each of which is made of fired refractory and arranged in direct abutment on the conical face of the punch and the bore of the die, a pair of outer gaskets, which are made of material of intermediate hardness level and arranged in adjacency outside the inner gasket, and a pair of stopper rings of readily deformable but highly tough material and arranged in adjacency outwards to the outer gaskets. The high temperature high pressure apparatus is used in the production of synthetic diamonds or cubic boron nitride.
Frushour, in U.S. Pat. No. 5,244,368, discloses a high pressure/high temperature piston-cylinder-type apparatus having an electrically insulating diamond or cubic boron nitride coating disposed between one or both movable pistons and the surrounding core to electrically isolate the piston or pistons from the surrounding core. The electrically insulating coating is applied to the exterior surface of one or both of the pistons or, alternately, to the inner surface of the core. Electrically insulated, right circular cylindrical pistons are used at both ends of the apparatus resulting in the ability to uniformly compress reaction charges at high temperatures with a much higher length-to-diameter ratio. A ring of electrical insulating material is alternately mounted at the reaction charge end of each piston, with the remaining exterior surface of each piston coated with a thin, elastically insulating layer.
Burns et al., in U.S. Pat. No. 5,980,852, disclose a reaction vessel for use in producing large diamond crystals of good quality and yield including a reaction volume and a reaction mass located in the volume. The reaction mass comprises a plurality of seed particles located in or on a surface in the reaction volume and a carbon source separated from the seed particles by a mass of metallic catalyst/solvent for diamond synthesis. The mass comprises alternating layers of carbon-rich and carbon-lean metallic catalyst/solvent which lie parallel or substantially parallel to the surface. There is also a mass of alternating layers of carbon-rich and carbon-lean metallic catalyst/solvent within the volume.
Sumiya et al., in U.S. Pat. No. 6,030,595, disclose a high purity synthetic diamond with less impurities, crystals defects, strains, etc., in which the nitrogen content is at most 10 ppm, preferably at most 0.1 ppm and the boron content is at most 1 ppm, preferably at most 0.1 ppm or in which nitrogen atoms and boron atoms are contained in the crystal and the difference between the number of the nitrogen atoms and that of the boron atoms is at most 1×1017 atoms/cm3. The strain-free synthetic diamond is produced by a process for the production of a strain-free synthetic diamond by the temperature gradient method, which comprises using a carbon source having a boron content of at most 10 ppm and a solvent metal having a boron content of at most 1 ppm and adding a nitrogen getter to the solvent metal, thereby synthesizing the diamond.
However, the apparatuses currently used for producing synthetic diamonds and other ultra-hard materials by way of the application of high pressure and high temperature do not always provide the necessary reproducibility and quality of the gemstones due to the problems discussed above with respect to the dissolution of the seed material in the solvent catalyst and the presence of multiple nucleation sites. The loss of a production run for making a synthetic diamond results in lost product and lost profits since the time to produce a synthetic diamond is a number of days. Thus, it is important to be able to provide ideal production conditions in the apparatus in order to ensure growth of the synthetic diamond.
It is also important that the apparatus be able to withstand the pressures and temperatures associated with making the synthetic diamond. If the material from which the apparatus is made is too soft, the apparatus will deform when applying the pressure to the reaction core, making the apparatus unusable for future production runs. If the material does not have enough yield strength, then the apparatus will not return to its original shape following application of the pressure. Meanwhile, if the material is too brittle, the apparatus may crack upon application of the pressure to the reaction core. Thus, it is important that the material used to make the high pressure, high temperature apparatus have the necessary properties to withstand the pressures and temperatures over a large multitude of runs.